Heavy neutrino threshold effects in low energy phenomenology Original Research Article

Right-handed neutrinos with mass of O(1012 − 1013) GeV are required to implement the see-saw mechanism and generate neutrino masses capable of playing a role in structure formation. Moreover models of fermion masses often relate the Yukawa couplings involving these neutrinos to the up-quark Yukawa couplings. Here we study the effects of such couplings on the radiative corrections to quark masses. We find that b − τ equality at MGUT may still give the correct mb/mτ-ratio at low energies, but only if there is large μ − τ mixing in the charged leptonic sector. We propose specific mass matrix “textures” dictated by a U(1) family symmetry whose structure preserves mb = mτ at MGUT. In these schemes, due to the large νμ − ντ mixing, it is possible to give a simultaneous solution to the solar neutrino deficit and the atmospheric neutrino problem.